dectin-1 and TLR4 ligands in trained immunity

Dectin-1 and TLR4 mediated trained immunity and preclinical drug development

Vanderbilt University School of Medicine, department of Anesthesiology, department of Pathology, Microbiology and Immunology, Nashville, TN 37232

Research topic

Our research group is highly interested in understanding how toll-like receptor (TLR) and dectin-1 agonists modulate the host response to infection. We are currently funded by the National Institutes of Health to study the immunomodulatory properties of diverse TLR agonists and dectin-1 ligands with interest in understanding the molecular mechanisms by which these agents modify the host response to infection and translating our findings to improve the treatment of patients with infection.

Our research in trained immunity is focused in three primary areas.

Project 1. In a series of recent papers, C. albicans glucan was used to induce "metabolic reprogramming and trained immunity" and to increase resistance to infections(1-3). The C. albicans glucan used as the immune training agent in those studies was isolated in the Williams laboratory at East Tennessee State University and is a useful reagent for elucidating the trained immune phenotype. However, C. albicans glucan is a natural product that has a complex molecular structure and composition, it is not soluble in water and it is very high molecular weight (>500,000 Da). These and other characteristics make C. albicans glucan and other natural product glucans unsuitable as drug candidates. Thus, we are studying the immunomodulatory properties of synthetic glucans produced by the Williams lab. The synthetic products are suitable to drug development and have high translational potential. We are working with the Williams lab to understand how these compounds modify the host response to infection with common pathogens at the cellular and molecular levels.

Project 2: In addition to our interests in dectin-1 ligands, we have a long standing interest in understanding how TLR ligands modify the innate immune response to infection, with a particular interest in TLR4 agonists. We established that treatment with TLR4 agonists confers resistance to common hospital acquired pathogens in mice and sheep (4-7). The protective effects persist for at least15 days, are independent of T and B lymphocytes and are mediated by neutrophils and macrophages. Most recently, we focused on macrophages due to their key role in orchestrating innate antimicrobial responses and found that augmentation of macrophage functions is a major factor contributing to augmented antimicrobial immunity after treatment with the TLR4 agonist monophosphoryl lipid A (MPLA). MPLA induces a macrophage phenotype characterized by increased size and granularity, heightened metabolic function, augmented phagocytosis and oxidative burst activity but attenuated pro-inflammatory cytokine production. MPLA prompts activation of mTOR signaling in macrophages and blockade of mTOR prevents the MPLA-induced antimicrobial phenotype. However, the contributions of mTOR-regulated transcription factors and metabolic substrates to the TLR4 agonist-induced macrophage phenotype remain unknown and are under active investigation in our laboratory.

Project 3: In addition to understanding the mechanisms by which TLR4 agonists augment antimicrobial immunity, our other major goal is to advance the pre-clinical development of TLR4 agonists as we progress toward clinical application of these drugs. Although MPLA is an effective immunomodulator, it is only clinically available as part of the proprietary ASO4 vaccine adjuvant system. To address that shortcoming, we formed a collaborative team to develop pure synthetic analogs of MPLA that possess potent biological activity. Phosphorylated hexaacyl disaccharides (PHADs) are the result of that endeavor. PHADs are synthesized de novo and are equipotent with MPLA as immunomodulators. Based on preclinical testing in mice, we have chosen 3-deacyl (3D)-PHAD as our lead compound because of its efficacy and high potential for clinical development. Studies are underway to advance the pre-clinical development of 3D-PHAD by testing its safety and efficacy in clinically relevant models of burn injury and pneumonia in sheep and mice as well as performing toxicology and formulation work to allow for a future Investigational New Drug (IND) application to the Federal Drug Administration (FDA) to allow for clinical testing and application